In U.S. Pat. No. 3,470,400 to Leon Weisbord and U.S. Pat. No. 3,479,536 to Frank A Norris, both of which patents are assigned to the same assignee as the present invention, there is disclosed a vibrating beam accelerometer. As taught by these patents, the accelerometer comprises a thin elongated piezoelectric vibrating beam member mounted to receive compressive and tensile forces along its length. The forces applied to the beam affect its natural frequency of vibration. The beam is driven by electric fields acting transversely of the beam by means of longitudinally spaced electrodes along the length of the beam. The change in the natural frequency of vibration is detected by appropriate circuitry which derives information therefrom to determine the acceleration on the device.
In the vibrating beam accelerometer described by the above-mentioned patents, there is a problem of finding a means to make the device immune from external vibration. Damping in accelerometers is usually accomplished by viscous shear of a compressible fluid. Such a damping method is not possible in VBA's taught by the prior art, since the vibrating beam transducer it employs must operate in a vacuum. Eddy current damping has been attempted in some devices but has been found to be impractical because not enough relative velocity exists between the proof mass and the case during vibration.